This type of driving assistance system is conventionally known. For example, Patent Literature 1 described later discloses technology of calculating time until arrival of an own vehicle at an intersection based on a distance between the own vehicle and the intersection and a vehicle speed of the own vehicle and transmitting a stop request to a brake system of the own vehicle so as to stop the own vehicle before the intersection when it is predicted that a traffic signal when the own vehicle arrives at the intersection is in an entry prohibition state (with red signal light). Patent Literature 2 described later discloses technology used in this type of driving assistance system, the technology of calculating maximum predicted required time to a stop position of the own vehicle and predicting a display state of the traffic signal when the maximum predicted required time elapses in consideration of an error upper limit of a current position of the own vehicle in addition to the distance to the intersection (between the current position of the own vehicle and the stop position before the intersection) and the vehicle speed of the own vehicle.